1. Field of the Invention
The present invention relates to the transmission of electrical power from a remote source to an electric motoroperated materials-handling land vehicle, and more especially to the supplying of electrical power to electrically operated mining equipment working within open pit mines to increase mine production.
2. Description of the Prior Art
Referring to FIG. 3, of the drawings, illustrative of the prior art, a cross section is shown through a typical terraced open pit mine 10 for mining copper ore, iron ore or coal or other minerals. Typically giant power shovels with huge capacity buckets, one of which is shown at 11, are used to scoop the ore into large trucks, one of which is shown at 12, which then transport the ore out of the mine on haul roads leading out of the mine pit along its sloping terraced sides to a crushing mill outside the mine. The shovels are powered by large d.c. electric motors which are supplied with electrical power through high voltage electrical power extension cables 13 from a central stationary power source 14 outside the mine pit. Since there are usually several power shovels working in the mine pit, the pit floor is strewn with several of the large power cables, which typically are 4 or 5 inches in diameter and weigh approximately 6 pounds per lineal foot. To prevent damaging such cables, it is important that they not be run over by the trucks, shovels and other heavy equipment working in the mine. Therefore pairs of portable towers 15 mounted on skids suspend the extension cables 13 over the various haul roads on the floor of the mine pit. However, whenever one of the shovels 11 must be moved to a new location within the mine, the portable towers 15 must first be shifted and the cables 13 lifted and moved manually by truck and equipment operators and other personnel working in the mine. At such times, which are frequent, ore production comes to a standstill until the shovel move is completed. It is estimated that a power shovel having a capacity of 120 loads per 8-hour shift actually produces only 70 to 80 loads per shift, 58 to 66 percent of theoretical capacity, because of the down time involved in moving cables, towers, and shovels.
Another problem with the present system of transmitting power to the mining shovel is that the power cable 13 is plugged into a receptacle in the stationary base 11a of the shovel 11 and must be conducted through a turntable 11b to the motor in the rotatable shovel housing 11c. This is done using a large copper ring (not shown) on a stationary portion of the turn-table and spring-loaded brushes on a rotatable portion. Because of operating conditions within the mine and the long hours of uninterrupted use of the power shovels, it is necessary to replace the spring-loaded brushes frequently, about every 30 days in normal use. This usually requires one full 8-hour shift to accomplish. Also, at least several times a year the copper ring itself must be replaced by jacking the housing up off the ring. This is a two- or three-day job.
Still another problem in the current use of power extension cables in open pit mining is the safety hazard that such cables present to mine personnel. Such cables if damaged or broken by mining equipment present a serious danger of electrocution to mine personnel because of the high voltages carried by such cables.
Thus the current practice of transmitting electrical power to the power shovels through a large, heavy electrical extension cable is extremely expensive in terms of lost production time and dangerous.
Thousands of dollars have been spent in engineering studies and in trying various experimental systems in attempts to solve the foregoing problems, all without success. Accordingly, there is a need for a solution to these problems in order to increase open pit mine production to a level much closer to its theoretical capacity using existing equipment.